The proposed study is divided in two parts. Part I is concerned with the location and distribution of labeled retinyl acetate in the seminiferous tubules subcellular fractions. Part II relates to an investigation of retinol binding receptor protein present in the subcellular fractions. In Part I labeled retinyl acetate mixed in rat serum will be injected into the femoral vein and incorporation of radioactivity will be determined in the seminiferous tubules and its subcellular fractions. In Part II of the study isolated seminiferous tubules will be incubated with labeled retinyl acetate and the retinol binding protein in the cytosol fraction will be isolated. Purification and characterization will be achieved by sephadex and exchange column chromatography.